The disclosure relates generally to turbomachine blade cooling, and more particularly, to a turbomachine blade having a cover plate including a radial cooling groove.
Modern turbomachine blades, such as those used in gas turbomachines, require extensive cooling. Deemed secondary to airfoil cooling, and often overlooked, is the region outside of the hot gas path, i.e., the shank and cover plates. The blade platform forms the inner surface of the hot gas path and isolates the shank and cover plates from the high temperature gas stream. The cover plates form one edge of the wheelspace boundary, through which cooler air is passed to purge the wheelspace and inhibit ingestion of hot gas from the hot gas path into the shank region.
A typical industrial turbomachine blade design includes a platform seal pin and radial seal pins to retard the ingestion of hot gas into the shank region. A typical radial seal pin is cylindrical and is designed to fit in a groove in the cover plate of the blade. To avoid binding under load, the blades are designed such that there is a small gap between adjacent blades. Under rotation, the pin extends and contacts the adjacent blade, forming a line of contact. Despite the use of radial seal pins, it is common to have leakage across the platform seal pin or through the gap between radial and platform seal pins. That is, the seal arrangement is not perfect and leakage paths exist through which some hot gas will penetrate into the shank region. One means of preventing ingestion of hot gases into the wheelspace is to pressurize the shank, i.e., to ensure that the pressure in the shank cavity is sufficient to inhibit leakage. While this arrangement is effective, this method increases the amount of required (e.g., compressor) flow dedicated to turbine cooling and reduces overall turbomachine efficiency. Because the capability of the turbomachine blade material decreases as metal temperature increases and because thermal gradients change the stress field in the turbomachine blade, control of shank and cover plate metal temperatures is desirable. The narrow radial passage through which purge air flows adjacent the radial seal pins provides negligible cooling to the shank and cover plate.